This invention relates generally to fuel injection systems for diesel engines and, in particular, to common rail diesel engine applications.
Direct diesel fuel injection systems use high-pressure fuel pumps to build up pressure for each injection cycle. Injection pressures of these systems are generally dependent on speed and fuel output. At relatively low engine speeds and fuel outputs, injection pressure falls off, producing a less-than-optimum fuel injection process for good combustion.
Common rail fuel injection systems maintain a constant pressure. They typically include high-pressure fuel pumps, driven by a cam separate from an engine cam, that force fuel into an accumulator, or common rail. Fuel from the common rail is fed through solenoid-controlled valves to selected injectors in individual engine cylinders. With this type of system, compression and injection are independent. The rate of fuel injection into the cylinders is a function the fuel pressure within the common rail; therefore, the rate of fuel injection may be effectively controlled by controlling the common rail fuel pressure.
Fuel transfer pumps are used to transfer fuel from a source to the high-pressure fuel pumps. Fuel transfer pump output control is typically limited to pressure regulator valves, and the work demanded of the transfer pumps is often in excess of what is necessary.
The common rail fuel injection system of the present invention includes a plurality of high-pressure, engine-cam-driven fuel pumps. Each pump has a fuel input port and a fuel output port. A common rail having a plurality of fuel input ports and a plurality of fuel output ports is also included, each of the engine-cam-driven fuel pump output ports being connected to a respective common rail fuel input port. A plurality of solenoid-controlled fuel injectors, each having a fuel input port, are also connected to the common rail, each common rail output port being connected to a respective fuel injector input port. A fuel transfer pump is connected between a source of fuel and each of the fuel input ports of the engine-cam-driven fuel pumps to supply fuel to the engine-cam-driven fuel pumps.
The fuel injection system also includes a plurality of pressure regulator valves. Each is connected to a respective fuel injector to limit the maximum fuel pressure within the fuel injector and to provide a path, in additional to the injection path, through which fuel flows to reduce injector temperature